1. Field of the Invention
The present invention relates to a photosensitive material for electrophotography and, more specifically, to a sensitized photosensitive material for electrophotography.
2. Description of the Prior Art
Widely used photosensitive materials for electrophotography can be represented by those of the function separated-type that are obtained by providing on an electrically conducting substrate a photosensitive layer which contains a charge-generating agent and a charge-transporting agent. The photosensitive materials of this type can roughly be divided into those of the type of a so-called single dispersion layer obtained by dispersing a charge-generating agent in a medium that contains a charge-transporting agent and those of the type of a so-called laminated layer obtained by providing on the electrically conducting substrate, the charge-generating agent and the charge-transporting layer in the order mentioned or in a reverse order.
As the charge-generating agent, there are used, in many cases, P-type charge-generating pigments such as phthalocyanine pigment and like pigment as well as N-type charge-generating pigments such as perylene pigment, azo pigment and like pigment. Generally, however, these pigments have poor balance in the spectral sensitivity. When use is made only of the N-type charge-generating pigment such as perylene pigment or azo pigment, in particular, sensitivity is low on the side of long wavelengths of from 600 to 700 nm and fogging occurs on a yellow-base paper. In designing a photosensitive material that can be used in common for the halogen source of light, fluorescent source of light and laser source of light, it is desired that the photosensitive material has panchromatic spectral sensitivity. There is, however, available no pigment that meets the above requirement, and technology has been proposed for using plural kinds of pigments as described below.
Japanese Laid-Open Patent Publication No. 222961/1990 filed by the present applicant discloses a photosensitive material of the laminated layer type in which a charge-transporting layer and a charge-generating layer are provided on an electrically conducting substrate in the order mentioned, by using, as charge-generating agents, an N-type pigment (dibromoanthanthrone) and a P-type pigment (metal-free phthalocyanine) at a ratio of from 40/80 to 90/10.
Moreover, Japanese Laid-Open Patent Publication No. 228670/1990 discloses the use of an X-type metal-free phthalocyanine in an amount of from 1.25 to 3.75 parts by weight in combination per 100 parts by weight of a perylene pigment.
In the case of the former proposal (Japanese Laid-Open Patent Publication No. 222961/1990) using the N-type pigment and the P-type pigment in combination, when the photosensitive material is positively charged by the corona discharge, an electric field established by the corona discharge acts upon the P-type pigment that is electrically in a neutral state, whereby thermal holes are injected into the charge-transporting layer from the P-type pigment to neutralize the negative electric charge induced on the side of the substrate. Besides, negative space charge exists in the charge-generating layer which is the outermost layer, and intensifies the electric field together with the positive charge on the surface of the photosensitive material to enhance the photocarrier generation efficiency. However, this effect is obtained only when the charge-transporting layer and the charge-generating layer are provided in this order on the electrically conducting substrate, which is not still satisfactory from the standpoint of improving the photocarrier generation efficiency. According to the above latter proposal (Japanese Laid-Open Patent Publication No. 228670/1990) which uses the N-type pigment and the P-type pigment in combination, the sensitivity to red light is improved to some extent. However, this photosensitive material in which the N-type pigment (X-type metal-free phthalocyanine) is added to the P-type pigment (perylene pigment) which is a main pigment, so that these pigments are simply dispersed together in a binder resin, is not still satisfactory from the standpoint of improving the photocarrier generation efficiency and is not still satisfactory, either, for being used in such applications as in a high-speed laser printer and the like.